Fix warning message in DefaultReporter spec
Fix warning message in DefaultReporter spec

We were seeing the following warning message in the `DefaultReporter`
spec:

    `raise_error` was called with non-proc object nil

The solution was to change the use of `should_not` to use an expectation
instead.

Change-Id: Ia1758ac8c6c64087807c153d270487e16c001093
Reviewed-on: http://gerrit.causes.com/40303
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@causes.com>
Reviewed-by: Shane da Silva <67fb7bfe39f841b16a1f86d3928acc568d12c716@brigade.com>

skateman/haml-lint,mzp/haml-lint